This invention relates to processes and systems for treating wastewater and more particularly to removing nutrients from wastewater in a wastewater treatment process.
The prior art has employed many devices and systems to process and purify water from industrial operations and municipal sources prior to discharging the water. Activated-sludge wastewater treatment plants (WWTP""s), which are well known in the art, have been most often utilized to address this problem. Additionally, many industrial and municipal water treatment plants utilize biological systems to pre-treat their wastes prior to discharging into the usual municipal treatment plant. In these processes, the microorganisms used in the activated sludge break down or degrade contaminants for the desired water treatment. Efficient process performance and control requires quick and accurate assessment of information on the activity of microorganisms. This has proven to be a difficult task in view of the wide variety of materials and contaminants that typically enter into treatment systems. Also, variations in the quantity of wastewater being treated, such as daily, weekly or seasonal changes, can dramatically change numerous important factors in the treatment process, such as pH, temperature, dissolved oxygen, nutrients and the like, alteration of which can be highly detrimental to proper wastewater treatment. Improperly treated wastewater poses serious human health dangers.
Various biological nutrient removal (BNR) processes are currently used in wastewater treatment plants to assist in contamination degradation. In a typical BNR process, contaminants in the wastewater, such as carbon sources (measured as biochemical oxygen demand or BOD), ammonia, nitrates, phosphates and the like are digested by the activated sludge in anaerobic, anoxic and aerobic stages, also known in the art. In the anacrobic stage, the wastewater, with or without passing through a preliminary settlement process, is mixed with return activated sludge (RAS).
In many wastewater treatment plants one anaerobic stage is arranged in the BNR process. In the anaerobic stage poly-P microbial species take up short chain carbonaceous nutrient and store this nutrient intracellularly most commonly as polyhydroxybutyrate (PHB). Microorganisms must expend energy to accomplish this uptake of soluble organics and formation of intracellular storage products. The energy is obtained anaerobically through the cleavage of high energy phosphate bonds in stored long-chain inorganic polyphosphates. This process produces orthophosphate that is released from the cell into solution in the anaerobic zone. In a subsequent oxic stage, a rapid uptake of soluble orthophosphate provides for the resynthesis of the intracellular polyphosphates. Previously stored PHB is also aerobically metabolized to carbon dioxide, water, and new cells. When solids are wasted from the treatment process, the orthophosphate taken up by the poly-P microbes results in up to four times the phosphorus removal in comparison to a conventional treatment process without an anaerobic zone.
In most wastewater treatment plants, one or several anoxic stages are arranged in the BNR process. In the anoxic stages, denitrifiers, i.e., microbial species capable of denitrification, utilize nitrate and/or nitrite as electron acceptors and consume some of the available carbon sources during the denitrification process. NOx is reduced stepwise to nitrogen gas and released to the atmosphere in the following manner:
NO3xe2x88x92xe2x86x92NO2xe2x88x92xe2x86x92NOxe2x86x92N2Oxe2x86x92N2
The nitrate is usually supplied by recycling a certain volume of wastewater from the end of the oxic stage back to the beginning of the anoxic stage.
One or several oxic stages are typically employed in BNR processes. In the oxic stage, air which contains about 20% oxygen or pure oxygen, is supplied so that a desired dissolved oxygen level is maintained. Autotrophic organisms, i.e., microbial species capable of using ammonia as their energy source, convert ammonia to nitrite and nitrate under aerobic conditions. The poly-P microbial species in the wastewater uptake phosphate from the water phase and digest their intracellular PHB and PHV storage products converting it into polyphosphate, a compound for energy storage. The polyphosphate pool of the poly-P microbial species is thus replenished and phosphorous is removed from the water phase. The phosphorous is then removed from the system by sludge wasting, which is well known in the art. Under aerobic conditions, the remaining carbon sources in the water phase are further digested by aerobic organisms.
As the degradation of the contaminants nears completion, the microorganisms and the treated water are led through a solid/liquid separation process where the biosolids are separated from the liquid. The biosolids are then either recycled back to the anaerobic/anoxic/oxic treatment processes, or removed from the treatment process as waste biosolids. Common devices used in the solid/liquid separation are clarifiers where biosolids are settled to the bottom and withdrawn by recycling pumps while clear liquid flows over discharge weirs at the clarifier surface. Air flotation devices are also frequently used in the solid/liquid separation process. These are commonly known in the art.
However, many of the current wastewater treatment plants require clarifiers which increase the amount of space utilized by the wastewater treatment plant, add to the initial capital costs and increase operating and maintenance costs. Also, such systems oftentimes utilize significant operator input, which adds additional costs and, as mentioned above, utilize recycling/return systems which increase the capital costs, as well as the operating and maintenance costs. Finally, there is a significantly increased hydraulic retention time (HRT) in the overall treatment process.
In one aspect the invention relates to a system for removing BOD and NH3 from wastewater including a first wastewater treatment tank T1 having a first tank inlet I1 and a first tank outlet O1 with a first tank membranous filter F1, a second wastewater treatment tank Tnxe2x88x921 operatively connected to tank T1 to permit wastewater to flow between tanks T1 and Tnxe2x88x921, and an Nth wastewater treatment tank Tn having an Nth tank inlet In and an Nth tank outlet On with an Nth tank membranous filter Fn operatively connected to tank Tnxe2x88x921 to permit wastewater to flow between tanks Tnxe2x88x921 and Tn.
There is also a NH4 detector AD1 connected to tank T1, a NH4 detector ADn connected to tank Tn, a TSS detector TD1 connected to tank T1, and a TSS detector TDn connected to tank Tn and an air supply connected to at least one of said tanks.
A controller connects to an air supply, inlets I1 and In, outlets O1 and On, NH3 detectors AD1 and ADn, and TSS detectors TD1 and TDn. The controller shifts between operational cycles C1 and C2, wherein in cycle C1, I1 and On are on, In is off and F1 is in a cleaning mode until AD1xe2x89xa7X or TD1xe2x89xa6Y, wherein X and Y are selected concentrations of NH3 and TSS, respectively, and wherein in cycle C2, In and O1 are on, I1 is off and Fn is in a cleaning mode until ADnxe2x89xa7X or TDnxe2x89xa6Y.
In another aspect, the invention relates to a system for removing nutrients from wastewater including a first wastewater treatment tank T1 having a first tank inlet I1 and a first tank O1 with a first tank membranous filter F1, an Nth wastewater treatment tank Tn having an Nth tank inlet In and an Nth tank On with an Nth tank membranous filter Fn, a second wastewater treatment tank T2 operatively connected to tank T1 to permit wastewater to flow between tanks T1 and T2 and having a second tank inlet I2 connected to inlets I1 and In, a third wastewater treatment tank T3 operatively connected to tank T2 to permit wastewater to flow between tanks T2 and T3, and an Nxe2x88x921 wastewater treatment tank Tnxe2x88x921 operatively connected to tanks T3 and Tn to permit wastewater to flow between tanks T3 and Tnxe2x88x921 and between tanks Tnxe2x88x921 and Tn, and having an Nxe2x88x921 tank inlet Inxe2x88x921 connected to inlets I1 and In.
The system also includes an NH3 detector AD1 connected to tank T1, an NH3 detector ADn connected to tank Tn, a TSS detector TD1 connected to tank T1, a TSS detector TDn connected to tank Tn, an NO3 detector ND2 connected to tank T2, an NO3 detector NDnxe2x88x921 connected to tank Tnxe2x88x921, and an air supply and/or mixing device connected to at least one of said tanks.
A controller connects to the air supply mixing device, inlets I1, I2, Inxe2x88x921 and In, outlets O1 and On, NH3 detectors AD1 and ADn, TSS detectors TD1 and TDn, and NO3 detectors ND2 and NDnxe2x88x921. The controller shifts between operational cycles C1 and C2, wherein, in cycle C1, I1 and On are on, In is off, F1 is in a cleaning mode, and I2 and Inxe2x88x921 are on at j and k, wherein j and k are selected percentages of I1, until 1) AD1xe2x89xa7X or TD1xe2x89xa6Y or 2) NDnxe2x88x921+ADnxe2x89xa7Z, wherein X, Y and Z are selected concentrations of NH3, TSS and NO3+NH3, respectively, and wherein in cycle C2, In and O1 are on, I1 is off, Fn is in a cleaning mode, and Inxe2x88x921 and I2 are on at 1 and m, wherein 1 and m are selected percentages of In, and wherein the air supply is shut off in T2+1, when ND2xe2x89xa7A is in cycle C1 and in Tnxe2x88x922 when NDnxe2x88x921xe2x89xa7A is in cycle C2, wherein A is a selected concentration of NO3.
In yet another aspect, the invention relates to a system for removing phosphorus from wastewater including a first wastewater treatment tank T1 having a first tank inlet I1 and a first tank outlet O1 with a first tank filter F1, an Nth wastewater treatment tank Tn having an Nth tank inlet In and an Nth tank outlet On with an Nth tank filter Fn, a second wastewater treatment tank T2 operatively connect to tank T1 to permit wastewater to flow between tanks T1 and T2, a third wastewater treatment tank T3 operatively connected to tank T2 to permit wastewater to flow between tanks T2 and T3, an Nxe2x88x921 wastewater treatment tank Tnxe2x88x921 operatively connected to tanks T3 and Tn to permit wastewater to flow between tanks T3 and Tnxe2x88x921 and between tanks Tnxe2x88x921 and Tn, a PO4 detector PD1 connected to tank T1, a PO4 detector PDn connected to tank Tn, a TSS detector TD1 connected to tank T1, a TSS detector TDn connected to tank Tn, an air supply and/or a mixing device connected to at least one of the tanks, and a controller connected to the air supply mixing device, inlets I1 and In, outlets O1 and On, PO4 detectors PD1 and PDn, TSS detectors TD1 and TDn, and Filters F1 and Fn, the controller shifting between operational cycles C1 and C2, wherein, in cycle C1, the air is off in T1 and on in Tn, I1 and On are on and In and O1 are off until 1) PD1xe2x89xa6X or TD1xe2x89xa6Y or 2) PDnxe2x89xa7Z wherein X, Y, and Z are selected concentrations of PO4, TSS, and PO4, respectively, and wherein cycle C2, the air is off in Tn and on in T1, In and O1 are on and I1 and On are off until 1) PDnxe2x89xa6X or TDnxe2x89xa6Y or 2) PD1xe2x89xa7Z, wherein X, Y, and Z are selected concentrations of PO4, TSS, and PO4, respectively.